Nowadays, it is becoming a consensus that to utilize Li-ion batteries as energy storage is one of the best substitutes for limited, polluted and CO2-producing fossil fuels. Even though intensive research on Li-ion batteries has lasted a couple of decades, the development of electrode materials with high energy capacities still remains a big challenge.1-2 It is widely known today that one large family of compounds used as electrodes for Li-ion batteries are transition metal oxides and multi-metal oxides. This includes not only materials for cathodes such as LiMO2 (M=Mn, Co, and Ni), LiCoO2 has a theoretical capacity of 274 mAh/g. but also for anodes like Fe3O4, CuO among others.3-5 A new class of compounds that was explored as an alternative to oxides is obtained by introducing large polyanions of the form (XO4)y− (X=S,P,Si,As,Mo,W) into the lattice. An inductive effect of (PO4)3− and (SO4)2− ions raises the redox energies compared to those in oxides and also stabilizes the structure. For example, LiFePO4 has become a highly suitable electrode material due to its low price, high durability, and easy synthesis. It can reversibly intercalate Lithium at a high voltage (3.5 V) and has a good gravimetric capacity (170 mAh/g) which is an important attribute to produce a cell with a high energy density. Its analogues, for example LiMnPO4, are also good candidates for electrode materials (more specifically for positive electrode materials). Silicates of similar composition and crystal structure have also been considered for positive electrode materials. Most of the silicates investigated are of the form Li2MSiO4 where M2+ is a transition metal. Li2FeSiO4 may become another promising electrode material. But compared to LiFePO4, it has a lower electronic conductivity and a lower electrode potential2.
However, oxides and phosphates both have poor electronic and Li-ion conductivities, which can restrain the charge/discharge speed, as well as the cycling stability of such batteries. Enhancement of electronic and Li-ion conductivities is the key for improvement. Coating the particles of electrode material with conductors such as carbon or conductive polymers can lead to an improvement, especially in the case of a compound with such low conductivity. PPy coating improves the conductivity of LiFePO4 and increases the specific surface area of electrodes, PPy/PEG coating allows for easier access of ions and electrons to deeper lying LiFePO4 structure and improved electrochemical activity and charge-transfer reaction of cathodes39. A high increase of electrochemical performance was achieved for materials prepared with amorphous carbon coatings. However, adding large amounts of low density non-active materials like carbon or polymers to the active material, unfortunately results in a lowering of both volumetric and specific energy densities. Finally, doping with different additional cations is also considered to be an effective method. LiFePO4, for example, becomes a promising cathode material when cation-doping is used to make it a good conductor of both electrons and Li-ions. For instance, a Ni doped LiFePO4/C nanocomposite exhibits excellent electrochemical performance40. Improvements in reversible capacity have also been achieved when the iron phosphate was doped with Mg. This has been attributed to an improvement in electronic conductivity within the active material particles41. However, in the more general case, large series of optimization experiments are still needed in order to determine the proper types of cations and the proper concentrations.
Besides, another type of electrode materials, more specifically relevant to anodes, comprises transition metal nitrides, which include lithium insertion compounds, like e.g. Li3FeN2, Li3−xMxN (M=Co, Ni, Cu), Li7MnN4, as well as lithium free compounds, like e.g. CoN, Cr1−xFexN.6-12 Usually, nitrides have low work potentials because of the feature of covalent (or metallic) bonding between transition metal and nitrogen. However, recently it was realized that, in carbonate-based electrolyte batteries, anodes with a low work potential (<1V) could destroy the solid electrolyte interface (SEI) and thereby trigger short-circuits and electrolyte ignition during fast charge. These unwanted properties provide a strong motivation to search new anodic substitutes for graphite and nitride-like anode.1 To develop safe and long-life batteries, TiO2 and Li4Ti5O12 attracted more attentions and were investigated intensively for applicable anodes.13-14 Li4Ti5O12 showed a practical capacity as high as 200 Ah/kg and a proper potential plateau at 1.5V vs. Li+/Li0 resulting from the Ti4+/Ti3+ redox couple.3 Also, the Nb5+/Nb4+ couple had a potential around 1.5V vs. Li+/Li0 in niobates, and the further reduction to a Nb4+/Nb3+ couple may further increase the lithiation capacity of compounds. For examples, Nb2O5 and various niobates like AlNbO4, KNb5O13 and K6Nb10.8O30 exhibited outstanding electrochemical properties as anodes of Li-ion batteries.15-18 
Recently, studies have been started to probe transition metal oxidenitrides within various applications such as ionic conductivity, catalysis, pigment and thermoelectric.19-21 However, only a few of them were investigated as electrodes in Li-ion batteries. The first case that indeed a transition metal oxidenitride was used as an electrodes in Li-ion batteries was Li7.9MnN3.2O1.6, which exhibited a similar electrochemical behavior as Li7MnN4 but shows an improved chemical stability.22-23 It must be realized that, in principle, transition metal oxidenitrides are supposed to have higher theoretical capacity than the corresponding oxides because of their higher lithiation ability per unit weight. Unfortunately, the number of transition metal oxidenitride is quite limited due to the restricted ceramics sinter synthesis methods and difficult determination of N/O in structure. Up to now, the electrochemical investigation of transition metal oxidenitrides has mostly been focused on IVB, VB and VIB metals.24-25 
TaNO was documented in 1966 by Brauer for the first time and studied as new pigment recently.26 The oxidenitride anion of vanadium with 5+ oxidation state was discovered by ammonolysis only when Ba existed in structure.27 In contrast to that, NbNO was not accessible through a simple ammonolysis reaction. In 1977, single crystals of NbNO were grown by reacting NbOCl3 and excess NH4Cl at 900-1000° C. and used to identify its crystal structure.28 Also, it was reported that black powder of NbNO could be obtained by decomposition of niobium oxychloride amide. NbNO is iso-structural to TaNO: both compounds have the baddeleyite (ZrO2) structure with monoclinic symmetry(space group P21/c). As shown in FIG. 1, Nb atoms are surrounded by three oxygen and four nitrogen atoms to form irregular octahedral [NbO3N4] which are connected by edge-sharing N and corner-sharing O atoms. Electronically, Nb(V) oxidenitride owns semiconductor-like characteristics due to the fully empty d-band of niobium. NbNO has a calculated band gap of 1.7 eV and is supposed to show blue color.29 
The electrochemical performance of electrodematerials is still a crucial limiting factor for high energy density batteries and an increase of capacity is pivotal. Thus there is a great need for an improved electrode material and an improved rechargeable battery comprising such an electrode material, in particular a battery with high stability over many charging-discharging cycles and/or improved capacity.